Which wars had an disastrous effect on the roman replubic?

The civil wars had a disastrous effect on the Roman Republic because all of them resulted in a Dictatorship when the republican form of government was suspended. Sulla resiged, but only after he purged the senate and reorganized the judicial system. Caesar grew too power hungry and the senate was willing to oblige him. Octavian won the last civil war of the republican era and did away with it altogether by consolidating power into one man.